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ASCII
This is a cut-down version of the Wikipedia page. See User_blog:Enojado271/Imp_2_Map_Gen_Keys:_In_Summary#comm-2793 for its main relevance to . '''ASCII' ( ), abbreviated from American Standard Code for Information Interchange, is a character-encoding scheme. Originally based on the English alphabet, it encodes 128 specified characters into 7-bit binary integers as shown by the ASCII chart on the right. The characters encoded are numbers 0'' to ''9, lowercase letters a'' to ''z, uppercase letters A'' to ''Z, basic punctuation symbols, control codes that originated with Teletype machines, and space. For example, lowercase e'' would become binary 1100101. ASCII codes represent text in computers, communications equipment, and other devices that use text. Most modern character-encoding schemes are based on ASCII, though they support many additional characters. ASCII includes definitions for 128 characters: 33 are non-printing control characters (many now obsolete) that affect how text and space are processedInternational Organization for Standardization (December 1, 1975). "The set of control characters for ISO 646". ''Internet Assigned Numbers Authority Registry. Alternate U.S. version: http://kikaku.itscj.ipsj.or.jp/ISO-IR/006.pdf. Accessed 2008-04-14. and 95 printable characters, including the space (which is considered an invisible graphic"RFC 20: ASCII format for Network Interchange", ANSI X3.4-1968, October 16, 1969.Mackenzie 1980, p. 223.). The IANA prefers the name US-ASCII. ASCII was the most common character encoding on the World Wide Web until December 2007, when it was surpassed by UTF-8, which includes ASCII as a subset. Organization The code itself was patterned so that most control codes were together, and all graphic codes were together, for ease of identification. The first two columns (32 positions) were reserved for control characters.Mackenzie 1980, p. 220, Decisions 8,9. The "space" character had to come before graphics to make sorting easier, so it became position 20hex;Mackenzie 1980, p. 237, Decision 10. for the same reason, many special signs commonly used as separators were placed before digits. The committee decided it was important to support upper case 64-character alphabets, and chose to pattern ASCII so it could be reduced easily to a usable 64-character set of graphic codes,Mackenzie 1980, p. 228, Decision 14. as was done in the DEC SIXBIT code. Lower case letters were therefore not interleaved with upper case. To keep options available for lower case letters and other graphics, the special and numeric codes were arranged before the letters, and the letter "A" was placed in position 41hex to match the draft of the corresponding British standard.Mackenzie 1980, p. 238, Decision 18. The digits 0–9 were arranged so they correspond to values in binary prefixed with 011, making conversion with binary-coded decimal straightforward. ASCII was incorporated into the Unicode character set as the first 128 symbols, so the 7-bit ASCII characters have the same numeric codes in both sets. This allows UTF-8 to be backward compatible with 7-bit ASCII, as a UTF-8 file containing only ASCII characters is identical to an ASCII file containing the same sequence of characters. Even more importantly, forward compatibility is ensured as software that recognizes only 7-bit ASCII characters as special and does not alter bytes with the highest bit set (as is often done to support 8-bit ASCII extensions such as ISO-8859-1) will preserve UTF-8 data unchanged. ASCII control code chart Other representations might be used by specialist equipment, for example ISO 2047 graphics or hexadecimal numbers. ASCII printable characters Codes 20hex to 7Ehex, known as the printable characters, represent letters, digits, punctuation marks, and a few miscellaneous symbols. There are 95 printable characters in total. Collation of data is sometimes done in this order rather than "standard" alphabetical order (collating sequence). The main deviations in ASCII order are: * All uppercase come before lowercase letters, for example, "Z" before "a" * Digits and many punctuation marks come before letters; for example, "4" precedes "one" * Numbers are sorted naïvely as strings; for example, "10" precedes "2" An intermediate order—readily implemented—converts uppercase letters to lowercase before comparing ASCII values. Naïve number sorting can be averted by zero-filling all numbers (e.g. "02" will sort before "10" as expected), although this is an external fix and has nothing to do with the ordering itself. See also Notes References ;Footnotes ;Bibliography * External links * The ASCII subset of Unicode * * Scanned copy of American Standard Code for Information Interchange ASA standard X3.4-1963 *